1. FIELD OF THE INVENTION
The present invention relates to the core bar of steering wheels.
2. DESCRIPTION OF THE PRIOR ART
In core bars of conventional steering wheels for automobiles, almost all peripheral shapes of sections of the ring part are round, so that coating layers of polyurethane or the like applied on the periphery of the ring part are apt to move in the direction of sectional periphery of the ring part. For prevention of the movement, as adhesive is applied on the ring part. Therefore, construction of steering wheels requires a process for applying of an adhesive and further, quality control of adhesives is necessary. The above-mentioned conditions are the same both with hollow pipe-shaped core bars and with solid core bars.
Further, in some solid core bars, the ring part having a round section was worked into an odd-shaped ring part having e.g. a half-round section for the purpose of preventing the movement of a coating layer. The working, however, required large-scale working processes and devices, leading to an increase in manufacturing cost.
Conventional hollow core bars for steering wheels had a considerble large wall thickness of the ring part, which was about 1.6 mm for the core bar made of steel.
When the wall thickness of the ring part was further lessened to reduce its weight, there were possibilities of the ring part being crushed by an injection pressure in coating the part with a synthetic resin such as a polypropylene resin or a polyvinyl chloride resin by an injection molding method, so that it was difficult to realize such lessening of the wall thickness.